Some gas turbine and compressor rotors have historically been of a xe2x80x9cstackedxe2x80x9d construction, where a series of individual wheels and shafts are held together with sets of bolts extending axially through the stack. Tension in the bolts squeezes the wheels and shafts together, and friction forces then allow torque to be transmitted across the interface, without relying on shear strength of the bolts. Significant variations in flange face friction factors, bolt assembly, and operation of the machine can result in substantial variation in the torque-carrying capabilities of the rotors. Continued operation at elevated temperatures can result in stress relaxation of the bolts, further degrading the torque capacity of the rotor.
Limits to the torque capability of friction drive machines are being approached with the higher temperature operation associated with newer, high compression ratio and high firing temperature machines. Further, operation with low heating value synthetic fuels (xe2x80x9cprocessxe2x80x9d fuels) increases the feasible output from a given machine, without any changes to the rotor construction. If the torque requirements on the rotor exceed the actual capabilities, wheels will slip relative to each other, typically resulting in a corkscrewed, or xe2x80x9ccammedxe2x80x9d rotor. Unbalance resulting from this will cause the machine to shut down due to unacceptable vibrations, and require time consuming and costly rotor teardown and reassembly.
A number of different approaches in torque transmission, including friction, bolt shear, radial teeth combined with bolts, gear teeth on wheel faces combined with bolts, etc. have been applied in industrial gas turbines or other rotary machines but all have inherent disadvantages.
This invention provides a system for positive torque transmission between rotor stages (both turbine and compressor stages are contemplated), to enhance the torque carrying capabilities of industrial gas turbines and to reduce the variability of this capability. Introduction of such a system will also reduce the need for high compressive loads in the rotor stack, thus allowing reduction in bolt tension, and/or bolt diameter. This, in turn will result in increased bolt design margin and reduced dead loads to the rotor and a net stress or weight reduction.
In an exemplary embodiment, the invention consists of a series of axially extending xe2x80x9cknucklesxe2x80x9d machined in the adjacent wheels to be coupled. These knuckles interlock across a flange face. The knuckles themselves have no radial or axial interference, and are therefore used in concert with a rabbet joint that maintains radial concentricity of the rotor. Axial bolts are still required to hold the structure together, but since the knuckles carry circumferential loads (torque), high compressive loads are not required and bolt stresses or diameters may be reduced from current practice.
Accordingly, in its broader aspects, the invention relates to an axial torque coupling between a pair of adjacent rotating machine wheels comprising a first wheel having a first plurality of axially extending knuckles, the first plurality of knuckles spaced circumferentially in an annular array about the first face with first slots therebetween, and a second wheel having a second plurality of axially extending knuckles, the second plurality of knuckles spaced circumferentially in an annular array with second slots therebetween; and wherein the first plurality of knuckles are received in the second slots and the second plurality of knuckles are received in the first slots, each of the first plurality of knuckles engaging an adjacent one of the second plurality of knuckles only on a single radial surface.